Field
Embodiments of the invention generally relate to methods of removing a contaminant from a metal surface. More particularly, to methods of removing a post-etch residues from a metal surface.
Description of the Related Art
The continuous shrinkage of microelectronic devices such as capacitors and gates over the years has led to a situation where the materials traditionally used in integrated circuit technology are approaching their performance limits. Accordingly, a demand has arisen for decreasing the resistance of the gate electrode of a transistor used in a DRAM or flash memory. Although polysilicon is conventionally used as the gate electrode, polysilicon has the drawback that the sheet resistance is high. Therefore, as a metal having a low resistance value, high adhesion to a silicon oxide film and silicon itself, and high processability, it has been proposed to stack a refractory metal such as tungsten as the gate electrode.
To fabricate tungsten gate electrodes, the device must be dry etched at points in the manufacturing process. This includes interaction with bromine, fluorine and chlorine, among other harsh chemistries. These chemistries will leave some etch residues on the tungsten layer. These residues need to be removed because they can impact device performance. Therefore, an effective and yet non-destructive method of remove the post etch residue, i.e. abatement, is critical for the tungsten gate based device fabrication.
Conventional chemistries used for post-etch residue removal contain oxygen gas as the plasma source, which will result in substantial surface oxidation of the tungsten. Surface oxidation of the tungsten can lead to degradation of the gate electrical conductivity and subsequent increase of the gate critical dimension (CD). The addition of H2 to the oxygen gas etch has been reported to be able to reduce the surface oxidation of the tungsten. However, extended exposure to H2/N2 plasma is found to create sidewall damage to features formed in the tungsten, such as the tungsten gate. Furthermore, the H2/N2 plasma does not have the photoresist (etch mask) removal capability, which is required for tungsten gate etch process.
Therefore, there is a need for an improved method of removing or cleaning a substrate surface.